The present invention relates to magnetic anomaly detection, more particularly to methods, systems, and devices for offsetting, compensating, or counterbalancing magnetic noise associated with vehicles used to carry or deploy magnetic anomaly detectors such as magnetometers and gradiometers.
Magnetic anomaly detection (“MAD”) has been practiced in geological, military, and other applications, such as involving detection of ore or mineral deposits, shipwrecks, enemy submersibles, etc. According to conventional practice of magnetic anomaly detection, the magnetic anomaly detection vehicle is an unmanned vehicle equipped with a magnetic field sensor (e.g., magnetometer) or a magnetic gradient sensor (e.g., gradiometer). The unmanned vehicle is commonly either an unmanned aerial vehicle (e.g., a “UAV”) or an unmanned underwater vehicle (e.g., an “ROV” or a “UUV”), and can be either autonomous or remotely controlled/operated (such as by radio signals, or using an umbilical/tether). The magnetic field/gradient sensor is carried by the unmanned vehicle to suitable locations for detecting nearby magnetic anomalies. For instance, an unmanned underwater vehicle and its magnetic sensing instrumentation can be implemented to detect magnetic anomalies that are situated upon, or buried slightly below, the sea bottom.
The successful detection of magnetic anomalies can be significantly compromised by vehicular magnetic self-noise, i.e., magnetic noise emanating from the vehicle itself that houses and conveys the magnetic sensing instrumentation. For this reason, conventional practice of magnetic anomaly detection frequently includes a process for reducing magnetic measurement components that are attributable to vehicular magnetic self-noise. Conventional vehicular magnetic self-noise reduction seeks to largely remove, from the measurements taken by the magnetic sensing instrumentation, the magnetic manifestations originating from the sensor conveyance vehicle. A conventional process of magnetic self-noise reduction typically involves three main stages. First, the vehicular self-noise is mathematically characterized. Next, calibration data are collected to solve for compensation parameters in the mathematical characterization of the vehicular self-noise. Finally, the mathematical characterization and the compensation parameters are used to remove the self-noise from data while the sensor conveyance vehicle is conducting its mission.
The conventional approach to vehicular magnetic self-noise compensation takes into consideration the anomalous magnetic manifestations emanating from the sensor conveyance vehicle (i.e., the magnetic anomaly detection vehicle), but assumes that the magnetic manifestations surrounding the sensor conveyance vehicle are non-anomalous and thus can simply be considered to be the earth's magnetic field. This assumption is valid when the magnetic conditions in the nearby extravehicular environs are non-anomalous; in such situations, the only magnetic anomalies extrinsic to the scope of measurement inquiry that need to be accounted for are those associated with the sensor conveyance vehicle. However, the conventional approach may be inadequate for any application in which anomalous magnetic circumstances exist in the vicinity of and external to the sensor conveyance vehicle, because the conventional approach does not account for these other extrinsic magnetic anomalies. A notable example of a source of extrinsic magnetic anomalies that is unaccounted for by the conventional approach is a central control vehicle (e.g., a surface ship) in a coupled two-body system in which a sensor conveyance vehicle (e.g., a remotely operated underwater vehicle, or “ROV”) is tethered to or otherwise physically connected to the central control vehicle at a close distance.